Rotary valve multiple combustor pulse detonation engine

ABSTRACT

A pulse detonation engine is provided with several detonation combustors selectively coupled to an air inlet and fuel source by a rotary valve. The rotary valve isolates the steady operation of the air inlet and fuel system from the unsteady nature of the detonation process, and allows the fueling of some of the detonation chambers while detonation occurs in other detonation chambers. The fuel system may use a solid fueled gas generator.

This application is a division of application Ser. No. 08/045,771 filedon Apr. 14, 1993.

BACKGROUND OF THE INVENTION

(i) Technical Field

The present invention relates to intermittent combustion engines inwhich the combustion products are used as a motive fluid.

(ii) Background Information

Intermittent combustion engines in the form of pulse jet engines, suchas those in U.S. Pat. No. 2,930,196 to Hertzberg et al. and U.S. Pat.No. 3,008,292 to Logan, are known. Pulse combustion in these prior artengines is deflagrative in nature.

A deflagration combustion process results in propagation velocities onthe order of a few feet per second. A detonation process, by contrast,can result in propagation velocities on the order of several thousandsof feet per second.

The use of a detonation combustion process in an engine has beensuggested. For example, U.S. Pat. No. 4,741,154 to Eidelman shows arotary engine using a detonation process.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a pulse detonationengine with design and operational simplicity.

Another object of the present invention is to provide a pulse detonationpropulsion system with significant performance advantages in thesubsonic and supersonic flight regimes.

Another object of the present invention is to provide a pulse detonationpropulsion system that can operate at higher cycle frequencies and lowerinlet losses than previous intermittent combustion engines.

Another object of the present invention is to provide a pulse detonationpropulsion system with the advantage of storability.

The present invention achieves the above objectives by providing a pulsedetonation engine with several detonation combustors selectively coupledto an air inlet and fuel source by a rotary valve. The rotary valveisolates the steady operation of the air inlet and fuel system from theunsteady nature of the detonation process, and allows the fueling ofsome of the detonation chambers while detonation occurs in otherdetonation chambers. The fuel system may use liquid, gaseous, or solidfuel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a cross-sectional view of one embodiment of the pulsedetonation engine of the present invention;

FIG. 1B shows a cross-sectional view of an alternative embodiment of thepulse detonation engine of the present invention;

FIG. 2 shows a cross-sectional view of the pulse detonation combustorsand the manifold/rotor assembly of the pulse detonation engine of FIG.1;

FIG. 3 shows a cross-sectional view of another embodiment of the pulsedetonation combustors of the present invention;

FIG. 4 shows a bottom view of the pulse detonation combustors of FIG. 2;

FIG. 5 shows a top view of the rotor disk valve of the pulse detonationengine of FIG. 1;

FIG. 6 shows a side view of the rotor disk valve of FIG. 5;

FIG. 7 shows a cross-sectional view of the manifold/rotor assembly ofthe pulse detonation engine of FIG. 1;

FIG. 8 shows an enlarged cross-sectional view of the manifold/rotorassembly of FIG. 7;

FIG. 9 shows a top view of the fuel manifold of the pulse detonationengine of FIG. 1A;

FIG. 10A shows a top view of the air manifold of the pulse detonationengine of FIG. 1A;

FIG. 10B shows a top view of an alternative embodiment of a fuelingarrangement;

FIG. 11 shows a cross-sectional view of a combustor tube during fueling;

FIG. 12 shows a schematic representation of conditions within acombustor before fueling;

FIG. 13 shows a schematic representation of conditions within acombustor during fueling;

FIG. 14 shows a schematic representation of conditions within acombustor after fueling is complete;

FIG. 15 shows a schematic representation of conditions within acombustor at the initiation of detonation;

FIG. 16 shows a schematic representation of conditions within acombustor during the propagation of a detonation wave;

FIG. 17 shows a schematic representation of conditions within acombustor at the exit of a detonation wave;

FIG. 18 shows a schematic representation of conditions within acombustor during the propagation of rarefaction waves and the exhaustionof burned gases;

FIG. 19 shows a schematic representation of a combustor beforerefueling;

FIG. 20 is a graph showing flow properties within a detonation chamber,corresponding to a combustor at a stage as depicted in FIG. 16;

FIG. 21 is a graph showing pressure ratios as a function of detonationwave Mach number;

FIG. 22 shows a schematic representation of an embodiment of a mixingarrangement for use in the present invention;

FIG. 23A shows a top view of the inlet vortex generator of the mixingarrangement of FIG. 22;

FIG. 23B shows a top view of an alternative embodiment of an inletvortex generator; and

FIG. 24 shows a cross-sectional view of an alternative embodiment of thepulse detonation engine of the present invention, incorporating apre-mixer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A shows a cross-sectional view of one embodiment of the pulsedetonation engine of the present invention. The engine has two or morecombustors or detonation chambers 10, each of which has an elongated,tubular construction. The lengths of the combustors 10 extend parallelto each other, so that they each produce thrust in the same direction. Anozzle shroud 16 may be used at the outlet end of the combustors 10 tocreate a quasi-uniform exit flow.

The combustors 10 are fueled with air from an inlet air duct manifold 20and fuel from a fuel manifold 30. The inlet for the air duct manifold 20may be in the form of a simple normal shock inlet. The fuel manifold 30delivers fuel from a fuel source 31 which can be controlled by a valve32.

The pulse detonation engine of the present invention may use solid,liquid or gas fuel. For example, the fuel source may be a solid fuel gasgenerator which can be controlled by a gas generator control valve. Asshown in FIG. 1B, the fuel source may be a liquid fuel source 70 whichdistributes fuel to the combustors through a series of liquid fuel lines72 and fuel injectors 73 and which is controlled by a liquid fuelcontrol valve 71. One or more fuel injectors 73 may be used for eachcombustor. Depending on the choice of fuel, an oxidizer generator 35 maybe used.

The combustors 10 are coupled to the inlet air duct manifold 20 and thefuel manifold 30 by a manifold/rotor assembly 40. The manifold/rotorassembly 40 has a rotor disk valve 50 positioned between a fuel/airmanifold mounting plate 42 on the upper side of the manifold/rotorassembly 40 and a combustor mounting plate 43 on the lower side of themanifold/rotor assembly 40. The upper mounting plate 42 is coupled tothe air manifold 20 and the fuel manifold 30, while the lower mountingplate 43 is coupled to the combustors 10.

The rotor disk valve 50 is positioned for rotation between the upperfuel/air manifold mounting plate 42 and the lower combustor mountingplate 43. The rotor disk valve 50 has openings 51 (see FIG. 5) and isrotated by a rotor drive motor 41, so that it may alternately open andclose the passage between the fuel and air manifolds and the combustors.

An ignitor 15, which may be, for example, a spark plug, is arranged nearthe inlet end of each combustor 10. An impingement ring 63 may also bepositioned near the inlet end of each combustor 10 to assist in mixingthe fuel and air in preparation for detonation.

FIG. 2 shows a cross-sectional view of the pulse detonation combustors10 and the manifold/rotor assembly 40 of the pulse detonation engine ofFIG. 1. Each combustor 10 is in the form of an elongated cylindricaltube, with one end (the inlet end) attached to the manifold/rotorassembly. The combustors 10 are arranged concentrically about an axis ofthe cluster, with the lengths of the cylindrical tubes extendingparallel to each other. The illustrated embodiment shows four combustors(see FIG. 4); however, the engine is not limited to this number. It willbe appreciated that the combustor chambers can also have a non-circularcross-section. For example, the cross-section could be square orpie-shaped.

The combustors 10 may be constructed of a carbon/carbon matrix 14. Asshown in FIG. 2, the combustors 10 may have an inner coating 13 whichmay be, for example, ruthenium, arranged within the carbon/carbon matrix14.

Other constructions of the combustors 10 are within the scope of thepresent invention. For example, as shown in FIG. 3, each combustor 10may have a ceramic liner 11 which may be, for example, Si₃ N₄ or ZrO₂.The liner is arranged within a ceramic matrix composite wrap 12.Alternatively, the combustors may be constructed of a suitable hightemperature metal alloy, for example an alloy oftitanium/zirconium/molybdenum.

FIG. 4 shows a bottom view of the pulse detonation combustors of FIG. 2,showing the arrangement of the combustors about a common axis of thecombustor cluster. A separate ignitor 15, which may be, for example, aspark plug, is arranged near the inlet end of each combustor 10.

As an alternative to the spark plug 15 arranged near the inlet end ofeach combustor 10, a separate predetonation tube may be used to initiatedetonation. In an embodiment using this method, the separatepredetonation tube may be constructed as a small tube above themanifold/rotor assembly 40. The predetonation tube is fueled with fueland an oxidizer, and detonation is initiated therein by a suitableignitor. The predetonation tube is constructed to fire into the maincombustor 10 after the main combustor 10 has been completely fueled.

As will be explained later with reference to FIG. 11, detonation mayalso be initiated by using a predetonation zone in the primarycombustors 10. This collocated predetonation method can be achieved byinjecting a region of fuel mixed with an oxidizer.

The rotor disk valve 50 as shown in FIGS. 5 and 6 has two fueling portopenings 51; however, the rotor disk valve is not limited to thisnumber. The openings 51 are arranged circumferentially around the centerof the rotor disk valve 50, so that as the disk valve 50 rotates, theopenings 51 are selectively positioned above the inlet ends of thecombustors 10 for fueling. The distance of the openings 51 from thecenter of the rotor disk valve 50 corresponds to the distance of theinlets of the combustors 10 from the central axis of the combustorcluster.

In the illustrated embodiment, the openings 51 are arcuate in shape,defined by inner and outer concentric edges. The distance between theinner and outer edges (i.e. the width) of the openings 51 is selectedfor cooperation with the combustor inlets.

Solid portions 52 are arranged between the openings 51 of the rotor diskvalve 50. As the rotor disk valve 50 rotates, the openings 51 and solidportions 52 are alternately positioned above the inlet ends of thecombustors 10. Thus, fueling of a combustor 10 occurs when an opening 51is positioned over the inlet end, and a combustor may be fired when asolid portion 52 is positioned over the inlet end.

FIGS. 7 and 8 show cross-sectional views of the manifold/rotor assembly40 of the engine of FIG. 1. The fuel/air manifold mounting plate 42 islocated on the upper side of the manifold/rotor assembly 40 for couplingto the air manifold 20 and the fuel manifold 30. The lower combustormounting plate 43 is positioned for coupling to the combustors 10. Therotor disk valve 50 is arranged between the upper fuel/air manifoldmounting plate 42 and the lower combustor mounting plate 43. Each of thefuel/air manifold mounting plate 42, the lower mounting plate 43 and therotor disk valve 50 may be constructed, for example, oftitanium/zirconium/molybdenum or carbon/carbon.

Sealing elements 44, 45 and 46 are arranged between the parts of themanifold/rotor assembly 40. These sealing elements are arranged toprevent leakage of gases. They may be constructed, for example, of solidgraphite or carbon/carbon impregnated with graphite.

A series of tapered roller bearings 47 are positioned on the side of therotor disk valve 50 away from the combustors 10. Forces from thedetonation processes within the combustors 10 on the rotor disk valve 50are transferred via the bearings 47 to the manifold/rotor assembly 40.Thus, the bearings 47 allow transfer of pressure forces from the rotordisk valve 50 to the vehicle body during operation of the engine. Otherbearing arrangements are possible within the scope of the presentinvention.

FIGS. 9 and 10 show top views of the fuel manifold 30 and inlet air ductmanifold 20, respectively. Fuel is distributed from the gas fuelgenerator to each combustor 10 through individual fuel ducts 34. Eachindividual fuel duct 34 has a finger-shaped cross-section and ends at afinger-shaped port 33 which opens into the corresponding combustor 10.

The individual fuel ducts 34 are arranged partially within individualair ducts 24, which are shown in FIG. 10A. The individual air ducts 24distribute air from the inlet air duct manifold 20 to the combustors 10.Each individual air duct 24 ends in a circular air port 23 which opensinto the corresponding combustor 10. The finger-shaped fuel ports 33(shown in phantom lines in FIG. 10) are arranged within the air ports23. It will be appreciated that this arrangement allows each combustorto be "topped off" with air after it is fueled.

The finger-shaped fuel ports 33 shown in FIGS. 9 and 10A may also beconstructed so that they do not extend completely to either side of theair ports 23, as shown by the fuel ports 36 in FIG. 10B. Each fuel port36 may be constructed to have an elliptical cross-section centrallylocated and completely within the respective air port 23. It will beappreciated that when the fuel port 36 is displaced from the leadingedge of the air port 23 the combustors 10 may be flushed with air priorto fueling.

Having described the various components, the operation of the pulsedetonation engine of FIG. 1 is as follows. Fuel is distributed from thefuel source in a steady mode, and air enters the inlet air duct manifoldalso in a steady mode. Rotor drive motor 41 rotates the rotor disk valve50 between the fuel/air manifold mounting plate 42 and the lowermounting plate 43.

It will be appreciated by one skilled in the art that when liquid fuelis used, as illustrated in FIG. 1B, the fueling of the combustors willoccur through liquid fuel lines 72 and fuel injectors 73. The operationof the rotor disk valve 50 will serve to selectively fuel the combustorsin essentially the same way as in a gas or solid fueled engine, asdescribed below.

In the fueling arrangement illustrated in FIGS. 9 and 10 correspondingto the engine shown in FIG. 1A, as an opening 51 of the rotary valve 50moves into position over the inlet end of a combustor 10, air and fuelenter that combustor through the corresponding port 23, 33. As the rotordisk valve 50 continues to rotate, the trailing edge of the opening 51closes off the finger-shaped fuel port 33, while air continues to enterthe combustor 10 through a portion of the circular port 23 which remainsopen. Thus, the fuel-air mixture in the combustor is "topped off" withair, and any gaps that may exist in the system are filled with air. Theair acts as an additional insulation buffer to protect the rotorassembly and prevent pre-ignition of neighboring combustors.

In the embodiment illustrated in FIG. 11, the fuel port 36 isconstructed so that it is displaced from the edge of the air port 23 ateither end. With this construction, the combustor 10 may be purged withair before fueling and topped off with air after fueling.

The combustor 10 in FIG. 11 is shown just prior to closing of the rotorvalve 50. The rotor valve 50 rotates in a direction shown by the arrowA. In FIG. 11, an opening 51 has almost completely passed over the inletend of the combustor 10.

The zones illustrated in the combustor 10 in FIG. 11 depict the areasthat result from the fueling arrangement. When the leading edge of theopening 51 of the rotor valve 50 first opened the inlet of the combustor10, air (from the leftmost region shown at the top of FIG. 11) enteredthe tube to flush the combustor of any remaining burnt gases from theprevious cycle. This air is shown as the purge region at the bottom ofFIG. 11.

As the rotor valve 50 continued to rotate, the opening 51 was positionedbelow the air and fuel ducts, thereby creating the primary detonationzone illustrated in the center of combustor 10. Continued rotation ofthe rotor valve 50 opened an oxidizer duct connected to the oxidizergenerator 35. In the illustrated embodiment oxygen is used as theoxidizer, but other suitable oxidizers may be used. The introduction ofoxidizer created the pre-detonation zone illustrated adjacent the sparkplug 15 in FIG. 11.

As the rotor valve 50 neared closing and reached the position shown inFIG. 11, the opening 51 allowed only air (from the rightmost regionshown at the top of FIG. 11) to enter the combustor 10. This created thebuffer region illustrated at the top of the combustor 10, therebytopping off the fueled combustor with air.

With continued rotation of the rotor disk valve 50 past the positionshown in FIG. 11, a solid portion 52 between openings 51 is positionedto close off the inlet end of the fueled combustor 10. In theillustrated embodiment, the ignitor 15 corresponding to the fueledcombustor 10 is then fired in the predetonation zone to initiatedetonation. Other methods of initiating detonation, for example an arcjet, may be used.

Upon detonation, pressure forces will act upon all inner surfaces of thecombustors 10. The pressure differential from the inlet end to theoutlet end of each combustor 10, acting upon the rotor valve 50, willcontribute to the thrust of the vehicle. The combustors 10 may betapered so that pressure along the lateral inner surfaces of thecombustors will contribute to thrust. The transfer of the pressureforces from the rotor plate 50 to the vehicle structure occurs throughthe bearing load transfer system 47. Thrust may be controlled by varyingthe spark ignitor timing, valve rotation rate and fuel injection rate,for example, through a microprocessor controller.

It will be appreciated that while one set of combustors is being fired,another set of combustors is being fueled with fresh fuel-air mixtures.As the rotor disk valve 50 seals a set of opposing chambers fordetonation, it also opens the adjacent chambers for recharging.

The detonation cycle of the pulse detonation combustors 10 of thepresent invention can be described according to the fundamentalprocesses that occur within the combustors. The pulse detonationcombustor cycle is comprised of several distinct events or processes:

A. The detonation chamber is charged with fuel-air mixture;

B. The rotary valve seals the fueled chamber, and detonation isinitiated at the closed end;

C. A detonation wave travels through the closed chamber;

D. The detonation wave exits, and burned gases are exhausted; and

E. The rotary valve opens the chamber, and the chamber is recharged(while adjacent detonation chambers are fired).

The processes occurring within a single chamber 10 will be explainedwith reference to FIGS. 12 through 19, which show successive steps inthe combustion process of the pulse detonation engine of FIG. 1.

Initially, as shown in FIG. 12, the detonation chamber 10 contains gasat atmospheric pressure. A solid portion 52 of the rotary valve 50 sealsthe inlet end of the detonation chamber 10. At the start of the veryfirst cycle, the chamber contains air at atmospheric conditions. Inlater cycles, at the start of the cycle, the chamber will contain acombination of air and unexhausted detonation products. In those latercycles, the chamber will be at atmospheric pressure, but the temperaturecan be somewhat greater than atmospheric due to the presence of burnedgas (unless complete aspiration has occurred).

As shown in FIG. 13, the rotary valve 50 will be rotated to position anopening 51 over the inlet. As the valve is opened, a fuel-air mixture isintroduced into the chamber 10. As described above, the chamber may beflushed with air prior to fueling. The velocity of the fuel-air mixtureintroduced into the combustor 10 can be adjusted in accordance with acombustor flow Mach number which will maximize engine performance. Thepressure and temperature of the fuel-air mixture entering the combustor10 is at P1 and T1, corresponding to State One.

As the valve 50 rotates toward sealing the combustor 10, it is designedto inject a narrow air buffer at the top or closed end of the combustionchamber, as shown in FIG. 14. The air buffer prevents strong shocks frompropagating within the rotor valve assembly and causing neighboringdetonation tube pre-ignition. The buffer also serves to insulate therotor from the high temperature detonation products.

As shown in FIG. 14, once the combustor 10 is fueled and "topped off" byan air buffer, the rotor disk valve 50 rotates to seal the combustionchamber 10 in preparation for detonation initiation. Solid portion 52 ofthe valve 50 fully closes the combustor chamber when the downstreamfuel-air mixture is still at some finite distance from the open end ofthe chamber. The valve timing ensures that the fuel-air mixture and thedetonation wave reach the combustor exit simultaneously, thus preventingany of the mixture from escaping unused. For a point design, the lengthof the detonation tube near the exit which is not filled with fuel iscalculated from the overall length of the tube and the relativevelocities of the fuel-air slug and detonation wave.

FIG. 15 shows a detonation wave initiated immediately after the valvecloses, in the fuel-air mixture region near the closed end of thechamber and just beyond the air buffer region. As the detonation isinitiated, an expansion zone is created at the closed end. Rarefactionwaves illustrated in FIGS. 15 and 16 are generated at the closed end ofthe detonation chamber and proceed toward the exit. The rarefactionsoriginate at the closed valve according to the constraint that thefluid's velocity is zero at the closed end. The rarefaction wavestrength is determined by the amount of energy required to satisfy thatconstraint and decelerate the burned gas behind the detonation to zerovelocity at the closed valve face.

There are two contributions to the momentum of the burned gas: one fromthe initial transverse momentum of the fuel-air mixture duringinjection, and another from the momentum imparted to the burned gas asit is accelerated by the detonation. Even though the burned gases moveaway from the detonation wave at the speed of sound relative to the wave(Chapman-Jouguet conditions), their velocity will be in the direction ofthe exit with respect to the chamber walls.

The detonation will proceed toward the open end of the chamber at theChapman-Jouguet detonation velocity (V1) or Mach number (M1)corresponding to the temperature and pressure at State One. The regionahead of the detonation will contain the unburned gas at State One (T1,P1). Just behind the detonation wave, the burned gas will be atsignificantly higher temperature and pressure (State 2). Near the inletor closed end of the detonation tube, the burned gas will be at asomewhat lower temperature and pressure (State 3) than the burned gasimmediately behind the detonation. This is due to the expansionresulting from the rarefaction waves generated at the closed valve whichpropagate downstream (toward the exit) behind the detonation wave. Theremainder of the burned gas within the expansion region between thedetonation wave and the closed end will be at some condition (T and P)between States Two and Three.

When the detonation wave reaches the combustion chamber exit andexhausts, the chamber contains burned gas (i.e., combustion products) atelevated temperatures and pressures. Conditions vary along the length ofthe chamber from State 3 at the closed end to State 2 at the open end asthe detonation exits, as shown in FIG. 17. Pressure increases from P3 atthe valve to P2 at the open end. The velocity distribution variesaccordingly from zero at the valve face, to a high velocity at the exit.

As the detonation exits the tube, a pressure differential of P2-Patmexists at the open end. As illustrated in FIG. 18, this pressuredifference creates a series of rarefaction waves which propagate intothe tube and expel the burned gas. The rarefaction waves travel into thetube at sonic velocity which varies with temperature. The temperaturedistribution varies along the length of the detonation chamber anddecays with time as the burned gas is expelled.

As the gas resident in the detonation chamber expands, the transversepressure differential along the chamber diminishes with time. As shownin FIG. 19, chamber pressures eventually approach atmospheric and theexhaust velocity decays to zero. The chamber temperature can be somewhatgreater than atmospheric due to the presence of burned gas (unlesscomplete aspiration has occurred). The detonation cycle can then berepeated.

FIG. 20 shows the physics associated with a detonation wave createdwithin a closed tube. The horizontal axis of FIG. 20 corresponds to thedistance along the combustor. FIG. 20 depicts a stage in the detonationcycle corresponding to that shown in FIG. 16.

The detonation wave can be considered to be comprised of a strong shockwave, which triggers combustion, and a thin flame front or heat additionregion just behind the shock. The shock front moves at the detonationvelocity, V1 relative to the gas, and increases the pressure andtemperature of the gas from its previous values of P1 and T1. Anignition delay region whose thickness is dictated by the reactionchemical kinetics exists just behind the shock.

Once the chemical reaction begins, heat is added to the flow and thepressure decreases from the shock front pressure. The thickness of theheat addition region is determined by the total time required tocomplete the fuel and oxygen reaction. At this point the burned gas isat State Two. In accordance with a detonative process, the temperature,pressure, and density at State Two are significantly greater than atState One.

In closed tube detonations, an expansion region exists behind the heataddition region. The furthest downstream location of rarefaction wavesdelineates the beginning of the expansion region. Rarefaction wavesemanate from, and are most heavily concentrated at, the closed valvewhere the pressure P3 exists according to the zero transverse velocityboundary condition at the wall.

FIG. 21 shows the expected detonation pressure ratios as a function ofdetonation wave Mach number. Three pressure ratios associated with adetonation wave propagating in a tube with one closed end are depicted.P_(s) is the pressure just after the initial shock front and before heatis added to the flow (i.e., in the ignition delay region). P₂ is thepressure just after the heat addition region, and is somewhat lower thanthe shock front pressure. Finally, P₃ is the pressure at the closed endof the tube. This value has been decreased substantially from P₂ as aresult of the rarefaction waves behind the detonation wave.

One factor contributing to the characteristics of the detonation processis the method of fueling and selection of fuel. In addition to the useof solid fuel, described in detail below, liquid or gas fuel may be usedin the present invention. Examples of liquid fuels which may be used inthe present invention include, but are not limited to, liquid hydrogenand liquid hydrocarbons. A suitable gaseous fuel is, for example,hydrogen gas.

A preferred fueling arrangement of a pulse detonation engine accordingto the present invention uses a solid fuel gas generator, orpre-combustor, which produces a fuel-rich gas mixture. The gas generatorcan be designed and operated in at least two different modes. In bothcases, a fuel-rich mixture is generated, which, when mixed with air fromthe primary inlets, is burned in the combustion chamber.

The first mode is based on a fuel mixture that incorporates just enoughoxidizer to allow the fuel grain to burn or pyrolize. Control of thefuel flow is possible with a gas generator control valve located at thetop of the gas generator.

The second mode, hybrid gas generation, uses air from a secondary inletsystem to burn or pyrolize the fuel grain. The secondary air flow streamprovides oxygen to promote burning of the fuel solid inside the hybridgas generator. The burning liberates large quantities of unburned fuelwhich then forms the fuel-rich secondary flow stream. If the secondaryair flow is varied, by bleeding for example, the rate of pre-combustionis reduced and the quantity of fuel-rich gas entering the combustionchamber is lowered. A smaller quantity of fuel in the combustion chamberdecreases the stagnation temperature rise and results in a lower vehiclethrust.

The rate at which a fuel mixture is produced in either gas generator isrelated to the fuel solid regression rate. The regression rate iscontrolled by the rate at which heat is transferred from a reaction or afree stream zone to the pyrolizing wall. The decomposition mechanism ismodeled using turbulent boundary layer theory. It predicts the magnitudeand the form of the contributing effects and provides an estimate of theexpected regression rates. Regression rates for solid fuels aredetermined experimentally. The gas generator flow rate is controlled bya gas generator control valve, such as valve 32 shown in FIG. 1.

The choice of fuels with the desired detonation properties is animportant aspect of detonation engine development. Example fuels for thepresent invention include, but are not limited to, aluminum (solid orvapor), magnesium (solid or vapor), carbon and simple hydrocarbons andpossibly boron.

Boron has ideal energy content, but boron particles produced by a gasgenerator are usually coated with an oxide layer which must first beremoved before the boron will ignite.

A fuel-rich gas based on aluminum can be generated without an oxidelayer. The aluminum particle size should be kept below 10 microns tomaintain a sustained detonation. Aluminum can also be generated as avapor which will further enhance its detonability.

Magnesium can be generated as a solid or vapor suspension, and can bedetonated. The magnesium particles or droplets must be approximately 10microns or less to detonate.

Both aluminum and magnesium vapor suspensions have very favorabledetonation properties. However, an undesirable property of the vaporsuspensions is their tendency to condense on cold surfaces because ofthe relatively high melting points of the two metals. Condensation ofaluminum and magnesium vapor can cause mechanical problems if it occurson tightly-fitting parts with small gap tolerances. Alternately thesystem could be heated by designing a gas generator fuel grain whichfirst produces hot gas followed by the fuel-rich gases.

Carbon has an energy content similar to aluminum. Carbon can begenerated as a solid suspension and will not condense on any enginesurfaces.

To ensure the optimum condition for fuel-air detonation, the fuel andair must be thoroughly mixed to ensure the fuel concentration is withinthe detonability limit (i.e., near stoichiometric). The components mustbe mixed to length scales comparable to the detonation phenomena lengthscales.

Mixing can be characterized on several levels including macroscopic andmicroscopic scales. Macroscopic mixing refers to the bulk fluidprocesses which bring the fuel and air components to close proximity(e.g., impingement of fuel and air streams). Microscopic mixing is theprocess by which the fuel and air are further mixed to a length scalerequired for detonation. Many techniques can be employed to producemicroscopic mixing. However, care must be taken to minimize totalpressure losses associated with these devices.

Several mixing strategies have been developed to ensure the necessaryfuel-air conditions exist within the detonation combustors of thepresent invention. As illustrated in FIG. 11, an air impingement ring 63may be used to direct the air stream to mix with the fuel. The ring 63has a tapered surface so that the air introduced at a radially outwardposition is directed toward the fuel introduced at a radially inwardposition. It will be appreciated that the air impingement ring 63 alsoacts to direct air for "topping-off" the fueled combustor tube and forpurging the combustor tube of remaining gases after firing.

As illustrated schematically in FIG. 22, when solid or gas fuel is used,fuel and air may be injected at the top of a detonative combustorthrough a serrated vortex generator 60 (macroscopic mixing) followed bya mixing mesh 61, injection ring or mixing module (microscopic mixing).The components of this mixing arrangement may be located in the top zoneof each detonation tube 10. A top view of the serrated vortex generator60 is shown in FIG. 23A. FIG. 23B shows an alternative serrated vortexgenerator 64 in which the fuel port is displaced on both the leading andtrailing edges from the edge of the air port.

Another mixing strategy involves mixing the fuel and air in a separatepre-mixer before injection of the fuel and air into the detonativecombustors. FIG. 24 illustrates this concept, with the pre-mixerindicated by reference numeral 62. The primary problem related to thepre-mixing concept is the potential of pre-ignition due to inadequateisolation of the mechanical elements of the engine. A variation of thisstrategy is to partially pre-mix the fuel and air to a fuelconcentration level just outside the fuel-air mixture's detonabilitylimits.

Electric power for the rotor plate motor, spark ignition system andother vehicle systems can be derived from several sources includingbatteries, inlet air or gas generator electric turbo generators, or acombination of these sources. Inlet air or gas generator systems consistof a turbine rotor, placed in either the air or gas generator flow, inorder to drive a small electric generator.

Materials should be selected dependent upon anticipated operatingconditions. It is expected that the engine material could be exposed topeak temperatures approaching 2500 K. and peak pressures of the order of20-40 atmospheres. Pressures just behind the detonation wave's shockfront (i.e., in the ignition delay region) are of the order of 40atmospheres, and pressure ratios across the entire detonation region areof the order of 20 atmospheres. The mode of operation will also exposethe structure to periodic variations of both a thermal and mechanicalnature.

Components made from carbon/carbon or titanium/zirconium/molybdenum (orsimilar alloy) may be used in construction of the pulse detonationengine of the present invention. For example, the detonation tubes andthe lower mounting plate of the manifold/rotor assembly could bemanufactured as one continuous piece of carbon/carbon composite. Therotor disk may also be fabricated using carbon/carbon composites.

Carbon/carbon can be machined to tolerances which produce surfacefinishes approaching the smoothness of machined metal. Carbon/carbon hasa very low thermal expansion coefficient and will allow the componentsof the engine to be assembled to very close tolerances, thus minimizingpotential sealing problems. Carbon/carbon fibrous materials aremanufactured by many companies.

Titanium/zirconium/molybdenum offers high temperature capability, iseasily machined, and is available from many specialty metal suppliers.

Several methods for initiating a detonation cycle may be used.Detonation may be initiated by igniting a fuel-oxygen mixture in a smalldetonation tube which discharges into a combustor, or by igniting afuel-oxygen mixture collocated within the combustor. Alternatively, ahigh voltage electric discharge or pyrotechnic ignitor can be used. Allthree approaches may be effective given fuel detonation characteristics,certain energy and power constraints.

The small detonation tube method requires fuel, an oxidizer, pumps, highspeed fluid valves, an electronic controller, a power supply and a sparkgenerator. The direct electric discharge method requires a spark plug,electronic controller and a power supply. Pyrotechnic ignition is viableif a small solid rocket is fired systematically into each combustor(e.g., through a small rotor or cylinder valve) to initiate detonation.

The choice of ignition method is dependent on engine size and on thecharacteristics of the fuel used. In order to keep the design of thepropulsion system as simple as possible, the direct electricdischarge/predetonator method and pyrotechnic ignitor are preferred.

What is claimed is:
 1. A solid fuel pulse detonation enginecomprising:at least one detonation chamber, having an inlet end and anoutlet end; a solid fueled gas generator; a fuel manifold for supplyingfuel from said solid fueled gas generator to said at least onedetonation chamber at said inlet end; an inlet air duct manifold forsupplying air to said at least one detonation chamber at said inlet end;and means for initiating a pulsed supersonic shock wave-triggereddetonation combustion wave in said at least one detonation chamber. 2.The solid fuel pulse detonation engine of claim 1, wherein said solidfueled gas generator generates a fuel-rich gas mixture, wherein saidfuel-rich gas mixture is generated by using an oxidizer to allow a fuelgrain to pyrolize.
 3. The solid fuel pulse detonation engine of claim 1,wherein said solid fueled gas generator generates a fuel-rich gasmixture, wherein said fuel-rich gas mixture is generated by hybrid gasgeneration, utilizing air from a secondary flow stream to pyrolize afuel grain.
 4. The solid fuel pulse detonation engine of claim 1 furthercomprising an air impingement ring near said inlet end of said at leastone detonation chamber for mixing said fuel and air.
 5. The solid fuelpulse detonation engine of claim 1 further comprising a serrated vortexgenerator and a mixing mesh for mixing said fuel and air.
 6. The solidfuel pulse detonation engine of claim 1 further comprising a pre-mixerfor mixing said fuel and air before injection into said detonationchamber.
 7. The solid fuel pulse detonation engine of claim 1 whereinsaid means for initiating a pulsed supersonic shock wave-triggereddetonation combustion wave comprises a spark plug.
 8. The solid fuelpulse detonation engine of claim 1 further comprising an oxidizergenerator and wherein said means for initiating a pulsed supersonicshock wave-triggered detonation combustion wave comprises a separatepredetonation tube which is supplied with an oxidizer from said oxidizergenerator.
 9. The solid fuel pulse detonation engine of claim 1 furthercomprising an oxidizer generator for supplying an oxidizer to saiddetonation chamber and wherein said means for initiating a pulsedsupersonic shock wave-triggered detonation combustion wave comprises aseparate predetonation region within said at least one detonationchamber created by supplying said oxidizer from said oxidizer generatorto said at least one detonation chamber.